Cell-state determination in phase-change memory

摘要

Methods and apparatus are provided for determining the state of a phase-change memory cell. A plurality of measurements are made on the cell, the measurements being dependent on the sub-threshold current-versus-voltage characteristic of the cell. The measurements are processed to obtain a metric which is dependent on the slope of the sub- threshold current-versus-voltage characteristic. The state of the cell is then determined in dependence on this metric which, unlike absolute cell resistance,is substantially unaffected by drift.